The construction, execution, and analysis of application- oriented simulations is difficult; the integration, coordinated execution, and after action review of heterogeneous distributed simulations can be overwhelming. Economy, risk mitigation, and just plain common sense compel us to utilize legacy simulations but discrepancies in controllability, fidelity, implementation paradigm, algorithms, representations, time management, construction, etc. tend to negate any potential gain. While several generations of interoperability approaches and associated standards have emerged and matured, even they have been limited in their ability to accommodate disparate classes of simulations. Within the permitted scope of this paper, a taxonomy for the most common interoperability issues (portcullises) for distributed simulation is developed. Part of this identification process will consist of establishing contexts and/or prerequisites for the issues, e.g. under what conditions are the issues actually issues at all. As a result, the prioritization will become application dependent. Methods for resolving the issues (battering rams), couched in the form of case studies, are subsequently presented to close the circle. Sources will include industry and government state-of- the-practice, academic state-of-the-art, and our own broad experience. Specific topics to be discussed include application philosophy, the integration of live entities, investigative versus analytical simulation, implications of human-in-the-loop, mixed and/or variable fidelity, heterogeneous time management schemes, current and emerging distributed simulation standards, simulation/exercise management, and control and data distribution. Discussion will focus heavily on examples and experience.